According to a conventional automatic wire-threading device, when a wire feed roller feeds a wire at a referenced speed and it is detected that wire-threading is completed by a signal of a detector, a control scheme of the wire feed roller is switched so that wire tension becomes equal to referenced tension (for example, Patent Literature 1).
Furthermore, to prevent disconnection of a thin wire electrode, automatic wire-threading is performed by a first unit that feeds a wire from a wire feed roller while opening a wire collecting roller, a second unit that closes the wire collecting roller after the wire is fed with a set distance, and a third unit that determines whether wire-threading is completed by detecting rotation of a roller while generating small tension in the wire (for example, Patent Literature 2).